Thermal-mechanical fatigue behavior of a cast K417 nickel-based superalloy

The thermal-mechanical fatigue (TMF) behavior of cast K417 nickel-based superalloy was investigated under in-phase (IP) and out-of-phase (OP) loading in the temperature range from 400 to 850°C. The results revealed that the tendency to cyclic hardening under thermal-mechanical and isothermal fatigue was higher than that under static tensile testing at 850°C. Isothermal fatigue (IF) was observed to cause higher cyclic flow stress than TMF. At a corresponding strain amplitude, the thermal-mechanical fatigue life was lower than that of isothermal fatigue, and the TMF life of out-of-phase cycling was higher than that of in-phase cycling. Scanning electron microscopic observations of fracture surfaces and longitudinal sections revealed intergranular fracture under in-phase TMF which led to the decrease in fatigue life.